Steam raising boilers and process for improving thermal efficiencies of such boilers



March 4,1969 w HALUWELL ETAL 3,430,610

STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OFSUCH BOILERS Filed Jan. 10, 1967 Sheet of 5 12, n FL 11 m ct March 4,1969 w, uw ETAL 3,430,610

STEAM RAISING BOILERS AND PROCESS FOR IMPROVING THERMAL EFFICIENCIES OFSUCH BOILERS Filed Jan. 10, 1967 I Sheet 2 of 5 Fig.3.

March 4, 1969 W. HALLIWELL ETAL STEAM RAISING BOILERS AND PROCESS FORIMPROVING THERMAL EFFICIENCIES OF SUCH BOILERS Filed Jan. 10, 1967 Sheet3 of3 5 Fig.4.

United States Patent STEAM RAISING BOILERS AND PROCESS FOR IMPROVINGTHERMAL EFFICIENCIES OF SUCH BOILERS Walter Halliwell, Bolton, and FrankPitts, Kersal, England, assignors to Magnesium Elektron Limited,Swinton, Manchester, England Filed Jan. 10, 1967, Ser. No. 608,407Claims priority, application Great Britain, June 3, 1966,

24,873/ 66 U.S. Cl. 122-479 7 Claims Int. Cl. F22g /00 ABSTRACT OF THEDISCLOSURE Disclosure This invention relates to stream raising boilersand a process for improving the thermal efficiencies of steam raisingboilers and, in particular, of oil-fired boilers in which superheattemperature cannot be achieved or can only be achieved at the expense ofintroducing excessive amounts of air into the combustion zone.

It is commonplace to convert to oil-firing boilers which have beendesigned for operation on solid or pulverised fuel or on gas and it isthen frequently impracticable, without major and costly reconstructionof the boiler, in particular of the combustion chamber, to attain themaximum superheat temperature which the construction of the boiler tubeswould permit without increasing the proportion of excess air used withconsequent loss of thermal efiiciency. It is known to overcome thisdifficulty by constructing refractory walls within the combustionchamber to shroud part of the wall tubes thereby reducing absorption ofheat in the combustion chamber and increase it in the superheaters.Another way of avoiding the need to use high proportions of excess airis to recirculate the cool combustion gases through the combustionchamber. In either case high costs of installation and maintenance areinvolved.

In the course of introducing particulate magnesium into boilercombustion chambersfor the purpose of controlling formation of sulphurtrioxide it has been observed that, under certain conditions, magnesiumis deposited on the wall-tubes of the boiler and that this phenomenon isassociated with a rise in superheat temperature although the excess aircontent of the combustion gases remain constant.

The object of this invention is to achieve a controlled increase insuperheat temperature without a simultaneous increase in excess air, orof permitting a reduction in excess air without reduction in superheattemperature.

According to this invention magnesium in the form of particles whichwill pass a sieve and will be retained on a 100 B5. sieve are injectedinto the boiler combustion chamber in a direction making an anglebetween 30 below the horizontal and 60 above the horizontal and in aplane (as seen in plan view) making an angle between 45 and 135 with thedirection in which the fuel is injected, in such manner that aheat-reflecting layer of magnesium oxide is maintained on the surface ofa predetermined section of the combustion chamber wall-tubes. The oilmay be injected from a plurality of ice fuel injection nozzles orburners in opposite directions or in the same direction while themagnesium may be injected in opposite directions across the fuelstreams. The position or each position of injection of magnesium in thecombustion chamber wall may be located between the levels of the lowestand of the highest banks of fuel injection nozzles or burners. Magnesiummay be injected at more than one position but in the case of eachinjection position the angles referred to are applied in relation to thedirection of fuel injection nearest to the position of magnesiuminjection. The velocity with which the magnesium particles are injectedand the size of the particles are preferably so chosen in relation tothe combustion chamber dimensions and the gas flow existing within thechamber that combustion of the particles is substantially completebefore the burning particles have fallen to a level below the lowestbank of oil burners and that no substantial proportion of the particlesis carried out of the combustion chamber before combustion of theparticles is complete.

The effect of this method of controlling the injection of magnesiumparticles is to produce a white deposit of heat-reflecting magnesiumoxide on that area of the walltubes lying between the plane of thelowest bank of oil burners and a plane situated below the position atwhich the combustion gases leave the combustion chamber and enter thesuperheaters or reheaters. The height of the band covered by magnesiumoxide is varied according to the desired increase in superheattemperature and/or reduction in excess air and can be controlled byvarying the velocity and angles of injection of the magnesium within thelimits specified. The increase of superheat temperature and/or reductionin excess air can also be varied by varying the reflectivity of themagnesium oxide coating which is controlled by varying the rate at whichmagnesium is injected. To achieve maximum economy, the velocity andangles of magnesium injection are varied by trial until the rate ofmagnesium injection is the minimum consistent with the desiredimprovement in thermal efiiciency.

The invention is illustrated by way of example in the accompanyingdiagrammatic drawings, wherein:

FIGURE 1 is a vertical section of an oil-fired boiler constructed inaccordance with the invention;

FIGURE 2 is a horizontal section on the plane 2-2 on FIGURE 1;

FIGURE 3 is a vertical sectional view of another form of boiler;

FIGURE 4 is a sectional view on line 4-4 on FIG- URE 3; and

FIGURE 5 is a sectional view on the line 5-5 on FIGURE 4.

A combustion chamber 10 is connected at its upper end by channel 8 tosuperheaters and/or reheaters 9. The chamber 10 is formed by four walls11, 12, 13, 14 and around all the walls are the usual water tubes 16.Oil burner nozzles 17, 18 extend through the walls into the chamber 10at an angle of to the plane of the wall in plan (FIGURE 2) so as toinject oil into the furnace in opposite directions. These nozzles inthis example are in four banks (FIGURE 1). Magnesium injection tubes ornozzles 20, 21, 22, 23 extend through the walls 11, 13 at an angle of 45to the vertical, their outer ends being lowermost, and at 70 to thewalls 11, 13 in plan and 20, 21 being at to nozzles 22, 23.

The magnesium oxide coating is produced on all four walls 11, 12, 13, 14between a plane indicated by broken line 25 in FIGURE 1 between thelower two banks of oil burner nozzles 17 and a plane indicated by thebroken line 26 which is below channel 8 through which the combustiongases leave the chamber 10.

In FIGURES 3, 4 and 5 the superheaters and reheaters 9 are above thechamber 10, the burner nozzles 17 enter the wall 14 in three banks, andthe magnesium injection nozzle 20 enters the wall 11 at right angles (inplan) to the burner nozzles 17 and a similar nozzle 21 enters the wall13 opposite to the nozzle 20 at the same angle to the vertical as inFIGURE 1.

Thus nozzles 20, 21 are directed oppositely to each other from oppositewalls of the chamber 10. Nozzle 20 is at right angles (in plan) tonozzles 17, and nozzle 21 is at 75 to nozzles 17. Nozzles 20, 21 are at60 to the vertical. The injection of the magnesium may be effected bymeans of the apparatus disclosed in our co-pending patent applicationNo. 22,963 of 1964.

Example Magnesium in the form of solid granules was injected at the rateof 3 lb. per hour into the combustion cham ber of a boiler consuming 12tons of crude residual fuel oil per hour. Before commencing injection ofmagnesium the boiler was operating with 7% excess air to producesuperheated steam at a temperature of 517 C., although the boiler hadbeen designed to operate at a superheat temperature of 525 C., usingonly 5% excess of air over the stoichiometrical amount required forcombustion of the fuel. After varying the particle size of the magnesiumgranules and the rate, velocity and angle of their injection it wasfound that injection of 3 lb. per hour of magnesium granules of meanStokes diameter /32" with a velocity of 150 feet per second in adirection at an angle above the horizontal of 30 and at right angles tothe direction of injection of the fuel produced an increase of 8 C. insuperheat temperature, thus attaining the maximum for which the boilerwas designed, this increase being achieved whilst operating with 5%excess air, a reduction of about 30% compared with the boilerperformance without magnesium injection.

Under these conditions, the heat-reflecting band of magnesium oxideextended for a height of about 20 feet from a position about 3 feetabove the lowest bank of oil burners to about 6 feet below the channelleading to the superheaters.

We claim:

1. In combination with an oil-fired steam raising boiler having acombustion chamber, water tubes lining the combustion chamber, asuperheater, the water tubes being in fluid communication with saidsuperheater, burner means for firing said chamber and magnesiuminjection means for introducing magnesium into said chamber, the processfor regulating the steam temperature of the boiler which comprises thesteps of injecting fuel in a generally horizontal direction into thecombustion chamber of said boiler, injecting magnesium particles whichpass a sieve and are retained on a 100 B.S. sieve into said combustionchamber in a direction to form an angle of between 30 below and 60 abovea horizontal plane through said chamber and in a direction to form anangle of between 45 and with the direction in which the fuel isinjected, thereby to form on the surface of a predetermined section ofthe combustion chamber walls a heat-reflecting layer of magnesium oxide.

2. The process of claim 1 wherein several banks of fuel injectionnozzles are provided, further comprising the step of verticallypositioning the magnesium injection nozzles in said chamber between thelowest and highest bank of fuel injection nozzles.

3. The process of claim 1 further including the step of varying thevelocity of injection and the size of the magnesium, particles inrelation to the combustion chamber so that combustion of the particlesis substantially complete before the burning particles have fallen to alevel below the lowest bank of burners so that no substantial proportionof the particles reach the superheater.

4. The process of claim 1 wherein the injection of magnesium particlesis at a rate of 3 pounds per hour at a velocity of feet per second atright angles to the direction of injection of the fuel.

5. In combination with an oil-fired steam raising boiler having acombustion chamber, water tubes lining the combustion chamber, asuperheater, the water tubes being in fluid communication with saidsuperheater, the improvement comprising a plurality of fuel injectionnozzles entering said chamber in a generally horizontal direction andmeans for injecting magnesium particles into said combustion chamber inthe region of said injection nozzles, said magnesium injecting meanscomprising a plurality of injection nozzles arranged at an angle ofbetween 30 below and 60 above a horizontal plane through said boiler andin vertical planes making angles between 45 and 135 with said fuelnozzles, whereby injection of said magnesium particles into said chamberforms on the surface of a predetermined section of the combustionchamber walls a heat-reflecting layer of magnesium oxide.

6. The combination of claim 5 wherein several vertically spaced banks offuel injection nozzles are provided, said magnesium injecting nozzlesbeing located and directed in said chamber to produce a layer ofmagnesium oxide on said chamber walls between the levels of the lowestand highest banks of fuel injection nozzles.

7. The combination of claim 5 wherein at least one of said magnesiuminjection nozzles is in a vertical plane at right angles to the verticalplanes of said fuel injection nozzles.

References Cited Reese et al.: Prevention of Residual Oil CombustionProblems by Use of Low Excess Air and Magnesium Additive, Journal ofEngineering for Power, April 1965, pp. 229-236.

CHARLES J. MYHRE, Primary Examiner.

